Cetyltrimethylammonium bromide (CAB) modified magnetic nanoparticles (Fe3O4@CTAB) were synthesized and used to remove arsenate from water. Fe3O4@CTAB was prepared by a modified simple co-precipitation process with cheap and environmental friendly iron salts and cationic surfactant CTAB. Powder X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infra-red spectroscopy were utilized to characterize the prepared adsorbent (Fe3O4@CTAB). Transmission electron microscopy (TEM) image showed that Fe3O4@CTAB particles were approximately spherical with the core size of 10 nm. With a saturation magnetization of 67.2 emu g(-1), the Fe3O4@CTAB nanoparticles could be easily separated from solutions with a simple magnetic process in very short time (within 5 min). Adsorption of arsenate on Fe3O4@CTAB reached equilibrium within 2 min at pH 6. Arsenate adsorption agreed well with pseudo-second order kinetic model and two-site Langmuir isotherm model with the arsenate adsorption capacity of 23.07 mg g(-1), which was twice greater than that of pure Fe3O4. Arsenate removal rate was over 90% at a wide pH range from 3 to 9 and the removal of arsenate was not obviously affected by the presence of dissolved natural organic matter (up to 10 mg L-1 as TOC) and competitive anions (sulfate, bicarbonate, and silicate up to 20 mg L-1, and phosphate up to 5 mg L-1) in solutions. Fe3O4@CTAB could be regenerated in alkali solutions and more than 85% As(V) was removed even in fifth regeneration/reuse cycle. (C) 2012 Elsevier B.V. All rights reserved.